Conventional baling of bulk products in general, and especially agricultural products such as grass, hay, silage or straw, comprises compressing the bulk material in the baling chamber of a baling apparatus to form a bale and subsequently wrapping the bale with a net or cover sheet, for example a protective film. By wrapping the bale with a protective wrapping, a controlled environment can be created within the bale. Such an environment may be aerobic or anaerobic. For instance, for the production of silage from grass, which requires anaerobic conditions, the protective film should provide a barrier against moisture, oxygen and UV light, and also provide mechanical protection of the bale. In other instances, such as wrapping of compostable waste, an aerobic environment may be desired.
Instead of round bales, large elongated bales have been popular for storing material such as fodder, hay, silage, etc. Such elongated bales are often formed using long tubes of plastic film, which are drawn over a preformed (compressed) bar of material. Alternatively, the material is pressed into the tubes. However, such tubes are inflexible and in practice limited to very few applications, since the dimensions of the tube are predetermined before starting the procedure of packing the material. Thus, if the material to be packaged is depleted before the plastic tube has been filled, the user has to cut off the tube before sealing the elongated bale. The left-over of the tube cannot be used for encapsulating another bar of material. This may result in large amounts of wasted plastic tubes and thus in unnecessary costs, since such plastic tubes are relatively expensive.
Also, the thickness of the plastic tube is predetermined. This is a disadvantage because depending on the intended application, such as production of silage, which requires high quality protection to achieve the anaerobic conditions, or simply weather protection, there are different requirements on the plastic tubes. For instance, production of silage requires a thicker plastic than weather protection. Furthermore, a more densely compressed material may require a thicker wrapping than loosely compressed or assembled bulk material. Due to the high price of polymeric materials, a plastic tube which is thicker than necessary for the application in question will result in unnecessary costs for the user and unnecessary use of plastic material, which is a disadvantage also from an environmental point of view.
Another problem with these tubes is that the form of the tube may affect the storage stability and the quality of the final product. If the base of the tube perpendicular its longitudinal extension is too narrow, the tube will collapse which causes formation of air pockets near the periphery of the bale resulting in the retention of moisture and oxygen in the bale, which is highly detrimental for silage production.
WO95/01716 discloses an apparatus for wrapping feed in plastic sheeting by progressively wrapping a sheet of plastic film around a bar of compressed feed, instead of threading a plastic tube around the feed. The apparatus comprises a movable frame, a feed receiving part in the frame as well as a plastic sheeting wrapping frame arranged to be rotatable around the feed to be wrapped. The apparatus further comprises a pressing screw or other means for compressing the feed into a continuous bar. The wrapping frame receives its driving force from a power transmission of a working machine, such as a tractor, via a revolving gearbox of the pressing screw. Thus, the revolving gearbox is coupled with a transmission of the working machine and to a transmission for revolving the plastic sheeting. Hence, the revolution of the plastic sheeting is dependent on the revolution of the pressing screw.
Even if the apparatus disclosed in WO95/01716 at least partly solves the problem of waste of plastic material due to left-over of tubes, there are several drawbacks with the apparatus described above. A problem is that the consumption of the plastic sheet is not controlled and cannot be influenced by a user of the apparatus. Furthermore, the rotation of the feed by the pressing screw makes the apparatus unsuitable for compressing large quantities of material comprising long straws, since the rotation of such material results in large friction forces at the periphery of the compression chamber. Another problem related to the rotation of the feed is that the apparatus is also unsuitable for handling material comprising very short straws, or particulate materials such as corn, since the rotation of these materials results in too low friction forces the periphery of the compression chamber, such that the material is not formed to a bar of sufficient density.
Therefore, there remains a need in the art for improved methods for wrapping bulk materials in general, and especially straw materials such as grass, hay or silage, as well as particulate materials, such that a controlled environment with desired properties within the wrapping is provided, and apparatuses used for this purpose.